Silicon nitride (SiN) is a widely used material in the manufacturing of integrated circuits (ICs). Due to its low reactivity and high thermal stability, silicon nitride is used as an insulating material, a mask material, an etch-stop material, a barrier material, a spacer material, etc.
Techniques for forming SiN include physical vapor deposition (PVD) and chemical vapor deposition (CVD), such as high temperature thermal CVD or plasma-enhanced CVD (PECVD). In one process, silane (SiH4) is reacted with ammonia (NH3) to form the SiN. Other silicon precursors may be used, such as silicon halides including silicon fluorides, silicon chlorides, silicon iodides, or silicon bromides. Examples of silicon halides include, but are not limited to, silicon tetrachloride (SiCl4) or dichlorosilane (SiCl2H2), trichlorosilane (SiHCl3), HSiI3, H2SiI2, H3SiI, H2Si2I4, H4Si2I2, or H5Si2I. To form high quality SiN, the PVD and CVD processes are conducted at high temperatures, usually greater than 750° C. However, these temperatures are not compatible with materials used in current ICs, some of which are thermally sensitive. Additionally, using a silicon halide as the silicon precursor is not desirable because reactive halide species, such as hydrochloric acid (HCl), are produced as byproducts. The reactive halide species are known to etch materials used in semiconductor fabrication, such as silicon-containing materials.
Atomic layer deposition (ALD) has also been used to form SiN. The silane, silicon halide, and ammonia CVD precursors are sufficiently reactive at high temperatures or in a plasma environment to form SiN by ALD. However, the precursors are not sufficiently reactive at low temperatures or without a plasma. While plasma-enhanced ALD (PEALD) has been used to form SiN and increased conformality and decreased deposition temperatures have been achieved compared to the conformality and deposition temperatures of CVD processes, step coverage of the SiN is not sufficiently conformal to cover complex topographies present in current ICs. In addition, excited species created during the plasma portion of the PEALD process are not selective to exposed materials on the ICs and, therefore, unintended reactions between the excited species and the exposed materials occur. Even in the absence of a plasma, the silicon precursor needs to be carefully selected to avoid these unintended reactions, which can result in degradation of IC performance.
Silylamine-based compounds, such as bis[(dimethylamino)methylsilyl](tri-methylsilyl)amine, bis[(diethylamino)dimethylsilyl](trimethylsilyl)amine, or tris[(diethylamino)-dimethylsilyl]amine, have also been proposed as silicon precursors for ALD processes.
As deposition requirements for SiN become more stringent, the techniques mentioned above have not been able to form SiN at the desired degree of conformality and at low temperatures.